1. Field of the Invention
This invention relates to a photographic support, and more particularly, to an improved photographic support for supporting a photographic image.
2. Description of the Prior Art
Conventionally, various plastic films are known as photographic supports such as cellulose acetate film, polyester film, polycarbonate film, polystyrene film, and polyolefin film. Among various characteristics required for a photographic support, oxygen permeability is of great importance. It has been found that low oxygen permeability of the support results in improved stability of the developed photographic image, especially high resistance to discoloration upon extended exposure to light, as well as stability with respect to the quality of a produced photographic film during storage.
The known photographic supports mentioned above do not have adequate oxygen barrier properties, and the idea of reducing the overall oxygen permeability by making a composite film having a polymeric material of low oxygen permeability on at least one surface of a support is described in Research Disclosure, No. 15162, November 1976. At page 82, in the left column thereof, materials such as polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose and alignate salt are mentioned. Polyvinyl alcohol has particularly high oxygen barrier properties under conditions of low humidity. However, these materials are hygroscopic, and when under conditions of high humidity (R.H. of at least 70%), their oxygen permeability increases significantly. In addition, when these materials are immersed in a wet photographic processing solution, they absorb much water and result in a photographic product which is difficult to dry. As a result, the total processing time is extended.
As described in Research Disclosure, supra, in the Journal of Polymer Science Symposium, Vol. 41, page 1, 1973 other materials are listed which are known to have low oxygen permeability, including polyvinylidene chloride, polycaprolactam, polychlorotrifluoroethylene, and polyvinyl chloride. Polyvinylidene chloride has oxygen barrier properties similar to those of polyvinyl alcohol, but a coating film thereof undergoes gradual dehydrochlorination during storage, and the hydrochloric acid generated adversely affects a photographic product using such film. A film of polyvinlyidene chloride turns to a yellowish brown color during storage, causing disadvantages in observing an image or performing exposure through such film. Polycaprolactam has inadequate oxygen barrier properties under high humidity. The oxygen barrier properties of polychlorotrifluoroethylene and polyvinyl chloride are about equal to those of polyester used as a known photographic support, and they are not sufficient to provide satisfactory oxygen barrier properties in combination with a polyester support.
As is clear form the foregoing, a photographic support with good oxygen barrier properties that is effective over a wide temperature range, is waterproof, does not emit any harmful gas, and is free from discoloration, has not yet been obtained.